Write and update data from xml file ?

Question

I want to create an xml file like the following format,

<Category>
  <Sales Title="SalesInvoice">
          <BillNo "Bill No">1220</BillNo>
          <BillDate "Date">1-1-2011</BillDate>
          <TotalAmount "Amount">15000</TotalAmount>
  </Sales>
  <Purchase Title="Purchase Invoice">
          <BillNo "BillNo">1</BillNo>
          <BillDate "Date">1-1-2011</BillDate>
          <TotalAmount "Amount">150</TotalAmount>
  </Purchase>
</Category>


Is any body know the C# code to create, select , and update the above xml file model please help me.



Thanking you,